181 - Ontogeny and contribution of cellular senescence to normal lung development

Poster Number: 181
Publication Number: 181.403

Hongwei Yao, Brown University, Providence, RI, United States; Monica Zhang, Brown University, Providence, RI, United States; Katy B. Hegarty, Brown University, Providence, RI, United States; Kurt H. Albertine, University of Utah, Salt Lake City, UT, United States; Phyllis A.. Dennery, The Warren Alpert Medical School of Brown University/Hasbro Children's Hospital, Providence, RI, United States

Background: During lung development, the mesenchymal lung compartment becomes thin to accommodate developing airways and air sacs, whereas the epithelium continues to proliferate. The developmental transition that allows for lung maturation is not fully understood. By imposing growth arrest, senescence limits the replication of old, damaged or unwanted cells. Previous studies show that senescence is a programmed mechanism that contributes to embryonic organ development across evolutionary distant vertebrates. However, the ontogeny and contribution of programmed senescence to normal lung development are unknown. 

Objective: We hypothesized that cellular senescence is a programmed cellular process, which facilitates normal lung development.

Design/Methods: Senescence biomarkers, including SA-β-gal, loss of nuclear lamin b1, p21 and p53 gene expression, were measured in mouse lung during the canalicular (E17.5), saccular (E19.5, postnatal day [pnd] 0, and pnd3) and early alveolar (pnd7) stages under normoxic condition. Expression of p21 and p53 genes was also measured in lamb lungs at 100, 130 140 and 150 days of gestation, which represent the canalicular, saccular, alveolar stages, and completion of alveolarization, respectively. A senolytic cocktail of quercetin and dasatinib (2.5 mg/kg and 2.5 mg/kg, i.p.) was administered into mice at pnd1 to evaluate the role of senescence in modulating lung development by measuring the numbers of alveoli and secondary crests, mean linear intercept, and radial alveolar count.

Results: In mice, senescence indicators (i.e., p21 and p53) gradually increased in the lung during embryonic development, peaked at pnd0, and then decreased significantly in the alveolar stage. SA-β-gal and loss of nuclear lamin b1 were also observed at birth and dramatically decreased throughout the postnatal saccular stage in mice. Similarly, in the lamb , lung p21 and p53 gene expression was increased at 130 days of gestation, compared to 100 days of gestation. These markers were lowest at term (approximately 150 days of gestation). Furthermore, in mice, reducing senescent cells at pnd1, using the senolytic cocktail quercetin/dasatinib, disrupted lung development, as indicated by decreased numbers of alveoli and secondary crests, a greater mean linear intercept and a lesser radial alveolar count at pnd7 compared to controls.

Conclusion(s):

Across species, in developing lungs, cellular senescence is most predominant during the saccular stage of lung development. We speculate that this orchestrates normal lung development.